A method for transmitting and recording signals covering a broad frequency band is known, for example, from German Pat. DE-PS 969 818 Ewerbeck. In the known method, the signal is split into several signals of narrow frequency width which are transmitted or recorded independently. In order to produce a plurality of signals equal in number to the number of available transmission channels, momentary values of the output signal are scanned with the aid of phase-shifted pulse trains. The chronologically correct recombination of the intermediate signals, which were transmitted or recorded in the individual channels, into the original signal, requires transmission of the scanning signal.
The known method is not suitable for the transmission or recording of frequency-modulated signals in which the momentary values of the signal differ only in frequency but not in amplitude. Carrier frequency based transmission of the intermediate signals is basically conceivable and would also lead to a reduction of the required bandwidth of the individual transmission channels for the intermediate signals as compared to the bandwidth required for transmitting a frequency-modulated output signal. However, the equalization of the necessarily large number of modulators and the appearance of phase errors during recombination of the intermediate signals into the original signal cause extraordinary difficulties. In particular, where the intermediate signals are stored in several tracks of a magnetic tape, inaccuracies of the tape movement lead to intolerable phase errors among the individual channels and prevent satisfactory demodulation of the intermediate signals and gap-free recombination.
Another system for decreasing the bandwidth requirement of a video recording and reproducing unit is known from the German published application DE-AS No. 22 37 255, to which U.S. Pat. No. 3,806,640, Furakawa, corresponds. As described there, a video signal containing arbitrary information is divided into a number of signals. These signals are recorded in several channels containing storage circuits. The video signal is shifted into a lower frequency range by performing the readout of the signal during a longer time interval than was used for recording. During reproduction, the recorded signals are again written into storage circuits and are then released in a shorter time interval than the write-in time interval. In this manner, the original time scale and the original video signal are restored.